Laninated curved beams

[Woodmatt]

I need to produce a number of curved beams,not sure how to describe them but they will be about a 3m span with a rise to the top of the curve of about 600mm.How would you all suggest making them and what size section.They are to produce a curved roof to a number of aviaries for birds so will not be carrying a huge amount of weight except if there is a lot of snow at any time. They will be similar to these but in timber http://www.aberglasney.org.uk/index.php ... news_id=69

 

[Chrispy]

I hope this link works if so it's a project I did a ago kind of shows making up just such rafters. https://www.ukworkshop.co.uk/forums/#p916646

 

[Giff]

Chrispy that link goes back to the homepage....or is it me ?

 

[Chrispy]

Lets try aagain https://www.ukworkshop.co.uk/forums/starting-another-what-is-it-i-m-making-now-quiz-t84179.html

 

[Woodmatt]

Thanks Chrispy that's very interesting and helpful,can I ask what size each lamination is and what the span was if you still remember.Thanks again.

 

[Chrispy]

Thanks Chrispy that's very interesting and helpful,can I ask what size each lamination is and what the span was if you still remember.Thanks again.

The laminations were cut from 2x4 par 5ths so would be 45mm wide and cut to about 15mm thick Ithink, the length must have been about 2.7m ish glued up they were 150mm wide so would be made up of 10 laminates, with that many I got very little sspring back.

 

[Giff]

I have made these for a Yoga school.I haven't any WIP pictures, but have made a jig from 18mm birch ply, with screwed down blocks (similar to Chrispy's, but because it is a tight curve I have blocks on the inside and outside of the curve and use a combination of clamps and wedges to pull it up. The timber is Ash and I use 8mm strips. It springs out a bit when unclamped, but pulls in again with the cross piece. Geoff

 

[woodfarmer]

make a backboard from planks and put pegs it it. bend the laminates around the pegs and hold it all together using wedges. I used to make curved bits like wheelhouse beams for boats.

A planar sawblade will produce a surface good enough to glue straight from the blade using either aerolite or cascamite.

 

[Woodmatt]

Thanks guys, originally I thinking I would laminate the beams the other way,in other words, across the beam,maybe three laminations about 15mm thick.Do you think this is not a good idea and would it not be as strong?

 

[Woodmatt]

Chrispy did you soak or steam the timbers before you bent them?

 

[Chrispy]

No steam just glue and cramps, it's only softwood so bends easily.
I don't think it would work very well with just three laminations tho, you will get a lot of spring back.

 

[Steve Maskery]

I think Matt means making up a flat sandwich, then cutting the curve out of it. There would not be any springback at all, as nothing is being bent.

If I've got that right, Matt, then, yes it would work, it would not be as strong but probably plenty strong enough.

Personally for bending I don't think you can beat doing it in a vac bag, although I admit that making a 4m bag is a bit pricey. The advantage of doing the flat sandwich way is that clamping can be done in stages, so you don't need a gazillion clamps.

 

[Woodmatt]

Sorry didn't explain myself very well,you're right Steve that was what I was thinking.There is not much money in the job and certainly not enough to go buying a load more cramps.I do like the idea of doing it Chrispy's way but I think it will need to do it as the sandwich particularly as I will be doing it on my own with no assistance so no one to "hold the other end" as it were.

 

[ColeyS1]

Here's how I did the curvy beam for my shed.

A ratchet strap wrapped right the way around would have the same effect.
Cause of the length I'd recommend a jig from shuttering ply sandwiched together so about 36mm thick

Cleaned up alright and didn't seem to move alot when the clamps were removed
Coley

Sent from my SM-G900F using Tapatalk

 

[Chrispy]

So you want to glue up a lump of wood 600mm + say 150mm or so for the depth of the rafter, 750mm in all that's a big glue up and an even bigger job of cutting out after, with a lot of short grain thrown in for good luck. laminate them I did mine on me tod, just get a good spreader and plenty of sash cramps.

 

[Steve Maskery]

No, Chris, that's not at all necessary.
You can make it "roughly" curved by making very obtuse mitres from, say 10" boards, but have three layers where the pieces overlap brick-wise to make a 3-ply faceted blank You can then refine the curve from there.

No mould required, maybe not even a template, although a template would help to cut the individual bricks out. I made an oval cheval mirror that way and it was very successful. Lots of long grain overlap for glue, very strong result. Virtually no short grain. Easy to manage single-handed, too.

IIRC I made an MDF template for the oval frame, made the centre layer first, gluing the ends together with superglue. Of course, that is not very strong so I screwed the template to that centre blank, a screw through every piece which made it much stronger. I then flush-trimmed it on the RT. I then glued the next layer on, staggering the joints and I could see to make sure that no part of it would be left uncovered. That made a fairly strong two-ply blank. I flush-trimmed that, too. Then I unscrewed the template and laid on the last layer, covering all the screwholes. I bet a similar technique would work on your larger scale.

I think a proper bent lamination would be best, but I think this is a very practical solution, also.

 

[Chrispy]

No, Chris, that's not at all necessary.
You can make it "roughly" curved by making very obtuse mitres from, say 10" boards, but have three layers where the pieces overlap brick-wise to make a 3-ply faceted blank You can then refine the curve from there.

No mould required, maybe not even a template, although a template would help to cut the individual bricks out. I made an oval cheval mirror that way and it was very successful. Lots of long grain overlap for glue, very strong result. Virtually no short grain. Easy to manage single-handed, too.

IIRC I made an MDF template for the oval frame, made the centre layer first, gluing the ends together with superglue. Of course, that is not very strong so I screwed the template to that centre blank, a screw through every piece which made it much stronger. I then flush-trimmed it on the RT. I then glued the next layer on, staggering the joints and I could see to make sure that no part of it would be left uncovered. That made a fairly strong two-ply blank. I flush-trimmed that, too. Then I unscrewed the template and laid on the last layer, covering all the screwholes. I bet a similar technique would work on your larger scale.
I know that both ways have a great deal of glue involved but seeing as this is going outside I feel that lamination would stand up to the weather better as there would be less conflicting movement in the layers of wood involved to break down the glue line.
I think a proper bent lamination would be best, but I think this is a very practical solution, also.